Different voltage displays on different charge controllers on same battery

[VictorAdebayo]

Dear Forum, my solar system is fixed with a 30amp SunMateSolar charge Controller and a 200amhr 12 volt battery. When the bars are full on the SunMate Solar (SMS) Controller it displays 12.7 volt as full battery. I have an idle smaller 20amp Controller, if connected to battery for testing(I don't have a digital tester), it displays 12.9 volt as the same battery voltage. I use gel battery.Which one is correct please and why the difference? Hope nothing is going wrong here then?

 

[Martaine2005]

Nothing is wrong and they both seem fairly accurate.
Average it as 12.8V.
Unless either unit has been properly calibrated, you won’t be able to tell which is closer to actual battery voltage.
But 12.7V vs 12.9V, I’d be happy with either.

Martin

 

[VictorAdebayo]

Oh ! Ok. Thank you. I have been worried, probably thinking one is overcharging and or one is under-functioning

 

[Martaine2005]

Nothing to worry about.
Even the same two meters will vary slightly.

Martin

 

[dave9]

I'd guess that the latter charger is applying current to the battery while taking the reading to result in the 0.2V higher value. You could check this with a multimeter.

If it is constantly supplying an extra 0.2V, that could result in shorter battery life long term from trickle charging more than it needs to. Considering the amount of this 0.2V, I wonder what would happen if you put a schottky diode in series... I mean besides it taking longer to charge.

 

[VictorAdebayo]

I'd guess that the latter charger is applying current to the battery while taking the reading to result in the 0.2V higher value. You could check this with a multimeter.

Thank you for your suggestion. I am trying to get a digital multimeter to no avail. The analog one I have is not helping matters. The reading during the day while charging are between 13.5(+ 0.2) to 14.3(+0.2). As I said, final settling of the battery at night is 12.6(+0.2)/12.7(+0.2).